Previous work has shown that the principal pathogenetic mechanism involved in inflammatory bowel disease is due to cell mediated immune mechanisms. Serum antibody may play a regulatory role by blocking the activity of lymphocytes sensitized to colonic antigens. During the coming year the reactivity of both specifically sensitized lymphocytes and lymphocytes which are engaging in a nonspecific cellular immune response within the walls of the colon will be investigated as two possible etiologies of ulcerative colitis. BIBLIOGRAPHIC REFERENCE: Rabin, B.S., Rogers, S.J. Pathologic changes in the liver and kidney produced by immunization with intestinal ntigens Amer. J. Path., 84:201, 1976.